New results in $\rho^0$ meson physics

Different ways to express the vector meson dominance (VMD) assumption are examined by analysing a wide set of data. These data cover e^+ e^- -> pi^+ pi^- and e^+ e^- -> mu^+ mu^- cross sections, the I=l=1 pi-pi phase shift and the near threshold predictions of Chiral Perturbation Theory (ChPT). We find that, of the models considered here, only that proposed by Bando et al. is able to consistently account for all information, provided one allows its parameter "a" to vary from 2 to 2.4. Consequently, we can propose motivated values for the rho mass and partial widths to pi^+ pi^- and e^+ e^- and for Br(omega -> pi^+ pi^-). As a consequence of allowing universality violation, we show that data provide evidence for a point-like coupling (gamma pi^+ pi^-) of magnitude ~ -e/6, while the common formulation of VMD excludes such a term